Day 3 vs Day 5 Blastocyst Transfers: There are very different schools of thought as to whether to perform a Day 3 or Day 5 Blastocyst stage embryo transfer. Not all Day 2 or 3 embryos can develop to a blastocyst with a loss of about 45 – 60% of your embryos as they are cultured the extra 2 or 3 days.